The present invention relates generally to a refrigeration system employing multiple economizer circuits to increase capacity and efficiency of the refrigeration system.
System capacity can be increased by increasing the subcooling of the refrigerant leaving the condenser. In a standard (non-economized) refrigeration system, the amount of subcooling typically ranges from 0 to 15xc2x0 F. An economizer can be employed to additionally subcool the liquid refrigerant exiting the condenser, increasing the capacity and efficiency of the refrigeration system.
In an economized system, the refrigerant is split into two flow paths after leaving the condenser. The first flow path is expanded to a low pressure by an expansion valve prior to passing into the economizer heat exchanger. The second flow path flows directly into the economizer heat exchanger and is cooled by the refrigerant in the first flow path. The refrigerant from the first path then flows along an economizer return path and is injected through economizer ports into the compressor. The vapor refrigerant in the second path is then expanded by a main expansion valve. By employing an economizer, both system capacity and efficiency is increased.
It would be beneficial to employ multiple economizer circuits to further increase the capacity of the refrigeration system. The benefits of employing multiple economizer circuits are especially pronounced for a refrigeration system operating with a high discharge to suction pressure ratio. Multiple economizers have not been employed in prior refrigeration systems as the refrigerant flow from each of the economizers mixes at the point of injection. For example, prior screw compressors include a pair of rotors. As only two rotors are employed, the rotational angle of the compression process is not large enough to prevent vapor communication among the suction port, the low pressure economizer port, the high pressure economizer port, and the discharge port.
The multiple stage economizer refrigeration system of the present invention includes a compressor, a condenser, a high pressure economizer circuit, a low pressure economizer circuit, expansion valves, and an evaporator. After the refrigerant exits the condenser, the refrigerant splits into two flow paths. The first path of refrigerant is expanded to a lower pressure in an expansion valve prior to flowing into the high pressure economizer heat exchanger. Refrigerant from the main path flows through the high pressure economizer heat exchanger and is cooled by the refrigerant in the first path. The refrigerant in the first path is returned to the compressor through the high pressure economizer port.
After being cooled in the high pressure economizer, the refrigerant from the main path again splits into two flow paths. Refrigerant in the second path is expanded to a low pressure in an expansion valve prior to flowing into the low pressure economizer heat exchanger. Refrigerant from the main path passes through the low pressure economizer heat exchanger and is cooled by the refrigerant in the second path. The refrigerant from the second path is returned to the compressor through the low pressure economizer port. Thus, additional subcooling of the main flow of the refrigerant is accomplished by subcooling in two stages. For even greater subcooling benefits, more than to stages can be implemented.
After being cooled in the low pressure economizer heat exchanger, the refrigerant is expanded in the main expansion valve, heated in the evaporator, and enters the compressor at the suction port. After compression, the refrigerant is discharged through the discharge port.
The multiple economizer refrigeration system can be employed in a screw compressor or a scroll compressor. The screw compressor includes a male rotor including a plurality of helical threads and a pair of opposing female rotors each including a plurality of helical threads. The helical threads of the male rotor engage the helical threads of the female rotors to create two sets of compression chambers. One set of compression chambers communicates with refrigerant from the high pressure economizer, and the other set of compression chambers communicates with refrigerant from the low pressure economizer.
Alternately, a scroll compressor is employed in the multiple economizer refrigeration system. Vapor refrigerant from the low pressure economizer is injected into the scroll compressor through a pair of low pressure injections ports. The low pressure ports are located such that vapor injection initiates shortly after the suction port is covered and the compression chambers are sealed from suction. Vapor refrigerant from the high pressure economizer is injected into the scroll compressor through a high pressure injection port. The high pressure injection port is located proximate to the discharge port. Refrigerant injection through the high pressure injection port and the low pressure injection ports occurs into separate scroll compressor pockets.
These and other features of the present invention will be best understood from the following specification and drawings.